1. Field of the Invention
This invention relates to an electrical component placing apparatus and placing method therefor and, more particularly, to eliminating pickup and placement mistakes of an electrical component by measuring the component thickness with a measuring unit to obtain an average thickness value, and regulating the rising or falling stroke of a component pickup nozzle based on the average value. This invention also relates to means for placing an electrical component by correcting a reference value for judging whether or not a pick and place head erroneously transfer and place another electrical component when transferring and placing the electrical component to a substrate by the pick and place head.
2. Description of the Prior Art
Conventional electrical component placing apparatus is adapted to rise or fall a nozzle of a pick and place head in an electrical component supply unit, to pick up an electrical component, and to pick and place the electrical component thus picked up on a substrate positioned by a positioning unit.
However, since the electrical component placing apparatus is operated at a high speed, the apparatus tends to frequently pick up erroneously the electrical component by a nozzle. One of the causes resides in an irregularity in the heights of the lower ends of the nozzles. Therefore, the present assignee has previously proposed the solving means (Japanese Patent Laid-open No. 1-261899 (corresponding to U.S. patent application Ser. No. 07/336,903), now U.S. Pat. No. 5,033,185. However, the causes of the erroneous pickup is not only the above-described ones but an irregularity in the thicknesses of electrical components. More specifically, since the same electrical components have molding errors, the thicknesses of the electrical components are irregular. If the thickness of the electrical component is excessively small, the lower end of the nozzle cannot be landed on the upper surface of the electrical component, and the nozzle fails to pick up the electrical component. On the other hand, if the thickness of the electrical component is excessively large, the lower end of the nozzle strongly impacts on the upper surface of the electrical component, and the component is damaged.
If the thickness of the electrical component is excessively small, even if the nozzle does pickup the component and moves it for placement on the substrate, the electrical component cannot be landed on the substrate. If nozzle suction is released before the electrical component is landed on the substrate, the electrical component is naturally dropped and there may be deviation of its; position on the substrate. If the thickness of the electrical component is excessively large, the electrical component landed on the substrate is pressed by the nozzle to be damaged. Further, when the pick and place head picks up the electrical component of the electrical component supply unit, the pick and place head might erroneously pick up another electrical component and pick and place the electrical component on the substrate.
In order to prevent the placing and picking failure of the electrical component as described above, the reference values of the sizes of the respective electrical components are registered in advance in a computer, the electrical component to be placed and picked on a substrate by a pick and place head is observed by a recognition unit such as a camera, whether or not the size of the electrical component measured by the recognition unit coincides with the reference value is judged by the recognition unit, the electrical component is picked and placed on the substrate as it is if the size of the electrical component coincides with the reference value, while the electrical component is paused to be picked and placed on the substrate if the size of the electrical component does not coincide with the reference value.
In the conventional means described above, it is necessary to register in advance the reference values of the sizes of the electrical components in the computer. Heretofore, the size of the electrical component is measured by a measuring instrument such as vernier calipers, and the measured value is registered as the reference value of judging good or no good of the size of the electrical component in the computer.
However, since such a method must measure a number of types of electrical components (up to 100 or more types in some cases) one by one by a manual work with the vernier calipers, a great deal of labor and time are required, and a measuring error and an inputting error to the computer feasibly occur. Further, even if the electrical components are of the same type, the respective electrical . components have an irregularity in the size due to their molding errors. Thus, even if the sizes of the electrical components measured by the vernier calipers as described above are registered as the reference values of judging good or no good of the electrical component in the computer, the reliability is low, and suitable judgement of good or no good of the electrical component cannot be performed.
The size of an electrical component described in a catalog or a product manual, etc., (i.e., catalog values) is heretofore registered as a reference value in a computer. However, in case of an electrical component of a special shape, the size described in the catalog is scarcely understood which of the portion of the component is pointed out, and an input error would feasibly occur. Since the electrical components have an irregularity in the size similarly to the case by the vernier calipers, the catalog values have low reliability as the reference value of the size of the electrical component, and cannot be employed as for judging good or no good of the size of the electrical component.